249 
tte 
n dans 
The techniques herein presented are based on conclu 
sions from over five years of simultaneous research efforts 
performed both in the laboratory and in the field. Other 
papers present details of the techniques while this paper 
concentrates on application to eutrophication classification 
with test sites in two geographic areas. One area is in 
Northern Minnesota with tannin lakes. The second area is in 
a 1- 
teriaux. 
v^getale 
cter des 
: experi- 
lation 
du lac. 
Southern Wisconsin with non-tannin lakes. 
METHODS 
The technique herein described was originally 
developed to determine from color and color infrared aerial 
photographs the quantitative amounts of paper mill pollution 
and inorganic siltation introduced into rivers and lakes. This 
irichment, 
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research work at the University of Wisconsin has shown that the 
brightness of a particular body of water on any aerial image, 
correlates remarkably well with the water quality parameter of 
turbidity caused by suspended matter in the water. The absolute 
brightness of a body of water however, is not only dependent on 
the material in the water, but is also a function of the amount 
of energy reflected back from the atmosphere, the surface of 
the water body, and the bottom of the water body where such 
water bodies are shallow and clear. If all the other sources 
remain constant and if there is a change in solids and turbidity 
within a water body this change in turbidity will correlate 
with the changes in brightness as shown on the aerial image. 
The correlation of laboratory reflectance to turbidity appears 
universal and constant. On the image, however, any change in 
the sunte position or in atmospheric scatter can cause a differ 
ent absolute level of image brightness from day to day and from 
frame to frame. Also, the correlation between turbidity and 
suspended solids changes as the size, shape, and other charac 
teristics of the solids change. 
ist such 
stance 
Lite (ERTS) 
caused by 
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Laboratory Analysis 
The laboratory analysis of collected water samples is 
performed using a spectroradiometer and an artifical light 
source that simulates the sun's energy. The water sample (about 
four liters) is placed in a 1 meter long tube and light is shown 
down from the top or up through the bottom of the tube depending 
on whether reflectance or transmittance values are desired 
(Scherz, et al., October, 1973). By comparing the energy reflect 
ed from the water to energy reflected from a barium sulfate